Small Changes In Refractive Index Research Articles

Effect of nanoparticle geometry on sensitivity of metal nanoparticle based sensor

Bio chemical detection using metal nanoparticles has been intensively investigated due to availability of robust nanoparticle synthesis methods whether chemically or using lithographic approach. SPR based sensor employs the shift of plasmonic resonance wavelength when local surrounding medium of metal nanoparticles change even slightly. The shift of the resonance wavelength depends sensitively on geometry and size of nanoparticle. The resonance wavelength and its shift were calculated numerically using boundary element method. Here, we compare the sensitivity of gold and silver nanoparticles to sense small change in refractive index of medium. Four different geometries (spherical, ellipsoidal, cylindrical, and donut-like nanoparticles) of different size were investigated to find the highest sensor sensitivity.

Design A Sensor Mach Zender Interferometer for the Detection of Chemical and Organic Substances Present In Food and Health Drinks

This Paper includes the nano cavity implementation of the biosensors in the detection of any chemical analyte and pesticide. Chemical, organic substances or any biological analytes are deemed to be present in any food or soft drink. Detection of these kinds of analytes are the potential risk. Photonic Crystals are rapid and precise to reach the sky for the next future. The photonic crystal model simulation is performed using Beam Propagation technology, with change in the refractive index in one selected arm. Therefore the designed MZI acts as a bio sensing device to detect any kind of chemical, bio analyte and organic substances that are present in different food. MZI has many advantages in photonic crystal with the use of least instrument and ready to be compatible with CMOS technology. The experimental program is observed for minute change in refractive index, in this work. Mach Zender Interferometer shall behave as sensor for small change in refractive index of pesticide value and observed power and intensity thus will be accounted. Indicates that it is highly sensitive for the changes in refractive index and in turn it can differentiate between normal food which do not contain any chemical and pesticide present in food.

Optimizing the Limit of Detection of Waveguide-Based Interferometric Biosensor Devices.

Waveguide-based photonic sensors provide a unique combination of high sensitivity, compact size and label-free, multiplexed operation. Interferometric configurations furthermore enable a simple, fixed-wavelength read-out making them particularly suitable for low-cost diagnostic and monitoring devices. Their limit of detection, i.e., the lowest analyte concentration that can be reliably observed, mainly depends on the sensors response to small refractive index changes, and the noise in the read-out system. While enhancements in the sensors response have been extensively studied, noise optimization has received much less attention. Here we show that order-of-magnitude enhancements in the limit of detection can be achieved through systematic noise reduction, and demonstrate a limit of detection of ∼ with a silicon nitride sensor operating at telecom wavelengths.

Study on the factors affecting the refractive index change of chalcogenide films induced by femtosecond laser

Femtosecond (fs) laser-induced functional microstructure in transparent chalcogenide film has potential application value in the field of novel infrared micro-nano photonic devices. Refractive index and thickness control of the film are crucial to manufacture infrared photonic devices. However, the changes of the refractive index and thickness induced by fs laser are too tiny to be characterized. In this condition, we designed and developed a method for studying the influencing factors of small refractive index changes induced by fs laser irradiation process. We obtained 64 different modified regions in chalcogenide film by using the laser direct writing technology. The transmission spectra of these fs laser-modified regions were recorded by use of micro-FTIR spectrometer. The refractive index and thickness of the transparent film before and after irradiation were calculated by an improved Swanepoel method. The dependence of the refractive index variation and the photo-expansion in the chalcogenide film on irradiation parameters (laser power and stage translational speed) was obtained quantitatively for the first time as far as our knowledge. The results show that the transparent chalcogenide film exhibits expansion and decreasing refractive index after fs laser irradiation. The transition threshold from non-thermal to thermal has been estimated for the Ge20Sb15Se65 film to be ~15.6 GW/cm2. There is a linear relationship between refractive index change and photo-expansion around the threshold. Raman spectroscopy analysis of the modified area suggests that the change of refractive index and thickness may be due to the reduction in glass network connectivity of the Ge-based film induced by fs laser.

Design of ultra-high sensitive biosensor to detect E. Coli in water

Escherichia coli (abbreviated as E. coli) are bacteria found in water, in food. The present work focuses applications of surface plasmon resonance (SPR) based biosensors to detect E. coli. SPR is a label-free technology that is used to detect biological samples. The SPR based biosensor design consists of optical wave guide with different structures of metal–dielectric interfaces and effort has been done to optimize design parameters for improved sensitivity. Metal-dielectric structures considered are Au–Si, Ag–Si, Au–GaAs and Ag–GaAs. Obtained simulation results indicates that the performance of the proposed sensor can be enhanced by varying the thickness and material of metal–dielectric interfaces. The device sensitivity obtained 1071.42 nm/RIU by considering metal-dielectric interface of Gold (thickness 0.074 μm) and Gallium Arsenide (thickness 0.22 μm). This result is significantly higher than sensitivity value of 250 nm/RIU found in published literature for similar type of sensor. From the simulation graph it is clear that for small change in refractive index (RI), value of 0.07 (1.33–1.4), there is significant shift in wavelength. This shows that the sensor is highly sensitive towards the change in RI and can be fabricated as lab-on-chip based biosensor. The optimized sensor was tested for detection for E. coli and sensitivity of 400 nm/RIU obtained. The design is compact and easy to fabricate using optical lithography as compared to the conventional optical component based SPR sensor.

Plasmonic versus All-Dielectric Nanoantennas for Refractometric Sensing: A Direct Comparison

In comparison to nanoplasmonic structures, resonant high-index dielectric nanoantennas hold several advantages that may benefit nanophotonic applications, including CMOS compatibility and low ohmic losses. One such application area might be label-free refractometric sensing, where changes in individual antenna resonance properties are used to quantify changes in the surrounding refractive index, for example, due to biomolecular binding. Here, we analyze and compare the sensing performance of silicon and gold nanodisks using a common and unbiased testing framework. We find that the all-dielectric system is fully capable of effectively monitoring small changes in bulk refractive index and biomolecular coverage, but the sensitivity is five to ten times lower than the plasmonic counterpart. However, this drawback is partly compensated for by a more linear response to adsorbate layer thickness changes and an approximately four times smaller susceptibility to photothermal heating. Finally, dielectric sensors may show promise if certain strategies are employed to improve their performance, which could thus bridge the gap between the two systems.

3D printed hand-held refractometer based on laser speckle correlation

Measurement of very small refractive index changes is very important from a material's characterization point of view. This paper demosntrates a compact, simple and accurate technique for measuring refractive indices of transparent liquids, based on Snell's law and laser speckle correlation. Furthermore, considering the cutting-edge technology of 3D printing and its ability to enhance a technique's functionality by providing a sturdy framework, a 3D printed hand-held device for measurement of refractive indices is also demonstrated. The device measures very small change in refractive index by measuring the change in the objective speckle pattern arising due to the change in laser light passing the liquid solution, which is caused by the apparent shift of a point source. Change in the speckle pattern is presented in terms of correlation coefficient which is computed by comparing a speckle pattern corresponding to distilled de-ionized water with that of the speckle pattern corresponding to a liquid whose refractive index is to be measured. This change in speckle pattern is related to the change in concentration which in turn is related to refractive index of the liquid. The device can measure changes in refractive index as small as 0.00038 with an average error less than 4.5%.

A Hi-Bi Ultra-Sensitive Surface Plasmon Resonance Fiber Sensor

In this paper, a simple, miniature, and highly sensitive photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor is proposed. The target analyte and the plasmonic material are at the outer surface of the fiber making practical applications feasible. A 30-nm gold (Au) layer supports surface plasmons. A thin titanium dioxide (TiO 2 ) layer is used to assist adhesion of Au on the glass fiber. The fiber cross section is formed purely by circular-shaped holes simplifying the preform manufacturing process. A high-birefringence (hi-bi) fiber is obtained by means of an array of air holes at the center of the fiber. A finite element method (FEM) is employed to analyze the surface plasmon properties of the proposed PCF-SPR sensor. By optimizing the geometric parameters, a maximum wavelength sensitivity (WS) of 25 000 nm/RIU and an amplitude sensitivity (AS) of 1411 RIU -1 for a dielectric refractive index (RI) range of 1.33-1.38 are obtained. Moreover, an estimated maximum resolution of 4 × 10 -6 and a figure of merit (FOM) of 502 are obtained that ensures high detection accuracy of small refractive index (RI) changes. Owing to its sensitivity and simple architecture, the proposed sensor has potential application in a range of sensing application, including biosensing.

Refractive Index Sensor Based on Micro- Structured Optical Fibers with Using Finite Element Method

In this paper a refractive index sensor based on micro-structured optical fiber has been proposed using Finite Element Method (FEM). The designed fiber has a hexagonal cladding structure with six air holes rings running around its solid core. The air holes of fiber has been infiltrated with different liquids such as water , ethanol, methanol, and toluene then sensor characteristics like ; effective refractive index , confinement loss, beam profile of the fundamental mode, and sensor resolution are investigated by employing the FEM. This designed sensor characterized by its low confinement loss and high resolution so a small change in the analyte refractive index could be detect which is could be useful to detect the change of the information of the biological molecule reaction and also in medical applications in fields like toxins, drug residues, vitamins, antibodies, proteins and parasites.

Applied magnetic field effect on core mode properties of MFPCF

The work investigates a magnetic fluid filled photonic crystal fibre (MFPCF) at 1557 nm under applied magnetic field. They computed the refractive index change of the MF due to the magnetic field and used it in simulations to find the effective refractive indices of the core and the first cladding modes of the MFPCF. Then, they analytically computed the effective mode area and the confinement loss. The effective refraction index of the core mode increasing by 0.0341% under the applied field of 0–500 Oe, increases the effective mode area by 128% and the confinement loss by 866%. Thus, a rather small change in the effective refractive index gives rise to a rather large change in confinement loss. However, this effect saturates after about 500 Oe because the MF nanoparticles no longer change their magnetic orientation. It is also noteworthy that the confinement loss changes almost linearly with the effective area as the magnetic field change. These results suggest that MFPCF are suitable for a tunable attenuator and a field sensor.

The Emerging Field of Quantum Based Measurements for Pressure, Vacuum and Beyond

The future of pressure, vacuum and even temperature measurement will employ lasers, Fabry-Perot optical cavities, cold atom traps and lots of quantum physics. For pressure measurement of a gas, photons interact at the quantum level such that light travels at a slower speed in gas than it does in vacuum. For extreme vacuum measurements, cold atom traps will be used to detect single collisions between gas trapped cold atoms enabling the number density of the gas to be measured. For temperature measurement is performed using silicon photonics to detect the small changes in refractive index in micro machined siliconphontoic cavities coupled to optical fibers. For dynamic pressure, NIST is developing a method where the unique quantum mechanical characteristics of the molecules are themselves the standard for pressure, making it consistent with the quantum-SI. Our approach is to use independent molecular spectroscopy as a dynamic measurement of pressure, where the pressure and temperature is ascertained by measuring time-resolved pressure-broadened spectra of CO molecules. This paper briefly reviews the status of these projects currently underway at the NIST Thermodynamic Metrology Group.

Metal-substrate-enhanced magnetic dipole resonance in metamaterials for high-performance refractive index sensing

In this work, we theoretically investigate metal-substrate-enhanced magnetic dipole resonance in metamaterials for high-performance refractive index sensing. The metamaterials are composed of periodic arrays of vertical U-shaped split-ring resonators, dielectric spacer, and metal substrate. Because the metal substrate blocks the transmission channel of light, the radiative damping of magnetic dipole resonance is nearly completely suppressed and thus its quality factor is increased noticeably. Owing to the narrow bandwidth, nearly-zero reflectance, and huge enhancement of electromagnetic fields at the magnetic dipole resonance, our designed metamaterial sensor has very high sensitivity (S = 1308 nm/RIU, S* = 26/RIU) and figure of merit (FOM = 52, FOM* = 1187). The good sensing capability allows for a much more sensitive detection of small refractive index changes and suggests potential applications in biosensing.

An interferometric optical fiber biosensor with high sensitivity for IgG/anti-IgG immunosensing

An immunosensor with low detection limit for detecting human-IgG (IgG, immunoglobulin G) is presented in this work. The sensor was designed using single mode fiber with large core-offset fusion splice based on Mach–Zehnder interferometer (MZI). The refractive index (RI) sensitivity is as high as 13936 nm/RIU in the RI range of 1.3328-1.3398, and the resolution of 1.44×10−6 is obtained. Afterwards, the sensing surface was immobilized with staphylococcal protein A and goat anti-human IgG to detect different concentrations of human-IgG, and a low detection limit of 47 ng/ml was observed. The proposed immunosensor has advantages of far simpler fabrication, high sensitivity, low detection limit, reusability and have promising potential for detecting small refractive index change in biological samples and application in biomedical field.

Nanoplasmonic Sensing from the Human Vision Perspective.

Localized surface plasmon resonance (LSPR) constitutes a versatile technique for biodetection, exploiting the sensitivity of plasmonic nanostructures to small changes in refractive index. The optical shift in the LSPR band caused by molecular interactions in the vicinity of the nanostructures are typically <5 nm and can readily be detected by a spectrophotometer. Widespread use of LSPR-based sensors require cost-effective devices and would benefit from sensing schemes that enables use of very simple spectrophotometers or even naked-eye detection. This paper describes a new strategy facilitating visualization of minute optical responses in nanoplasmonic bioassays by taking into account the physiology of human color vision. We demonstrate, using a set of nine different plasmonic nanoparticles, that the cyan to green transition zone at ∼500 nm is optimal for naked-eye detection of color changes. In this wavelength range, it is possible to detect a color change corresponding to a wavelength shift of ∼2-3 nm induced by refractive index changes in the medium or by molecular binding to the surface of the nanoparticles. This strategy also can be utilized to improve the performance of aggregation-based nanoplasmonic colorimetric assays, which enables semiquantitative naked-eye detection of matrix metalloproteinase 7 (MMP7) activity at concentrations that are at least 5 times lower than previously reported assays using spherical gold nanoparticles. We foresee significant potential of this strategy in medical diagnostic and environmental monitoring, especially in situations where basic laboratory infrastructure is sparse or even nonexistent. Finally, we demonstrate that the developed concept can be used in combination with cell phone technology and red-green-blue (RGB) analysis for sensitive and quantitative detection of MMP7.

Interrogation of coarsely sampled tilted fiber Bragg grating (TFBG) sensors with KLT

Tilted fiber Bragg gratings (TFBG) can be used as refractive index sensors, as their cladding modes, amplitude, and wavelength changes with the outer refractive index. However, as cladding modes have bandwidths that are narrower than the resolution of most infrared spectrometers, they can be detected only with an optical spectrum or vector analyzers. In this work, we demonstrate that through ad hoc implementation, the Karhunen-Loeve transform (KLT) algorithm can be used to demodulate a TFBG even using a coarse interrogator (156 pm), whereas cladding modes cannot be discriminated in the TFBG spectrum. We observe that the KLT output results are a reliable indicator to detect refractive index changes up to 1.85 ⋅ 10−3 refractive index units (RIU), down to a resolution of ~10−5 RIU. The KLT can be used to demodulate TFBG sensors and biosensors operating in small refractive index change conditions.

Active metasurface modulator with electro-optic polymer using bimodal plasmonic resonance

Electrically tunable metasurfaces have gained special interest as they can realize ultrathin surface-normal modulators in planar geometries. In this paper, we demonstrate a novel metasurface modulator based on electro-optic (EO) polymer that utilizes bimodal resonance inside a metallic subwavelength grating to increase the modulation efficiency. When two metal-insulator-metal (MIM) resonant modes are excited simultaneously inside the grating, they couple strongly to generate a sharp dip in the reflected spectrum. As a result, efficient intensity modulation with 15-dB extinction ratio can be obtained at the resonant wavelength under a small refractive index change of 8.5 × 10-3, corresponding to modulation voltage of less than 10 V. Due to the low parasitic capacitance of EO polymer and high conductivity of metallic gratings which is also used as the electrodes, the RC bandwidth of the device should easily exceed 100 GHz, potentially applicable to high-speed surface-normal modulators.

A biosensor based on plasmonic wave excitation with diffractive grating structure

We propose an active plasmonic device based on graphene. By using a diffractive grating on silicon, highly confined plasmonic waves in monolayer graphene are efficiently excited. The high electric field of the surface plasmons near the graphene layer makes them ideal for use in biosensors, where a very small change in refractive index should be detected. A small change in the refractive index of surroundings medium, induces a large change in resonant wavelength. The spectral shift per refractive index unit (∆λ0/RIU) of the sensor is considerable and exceeding 2000 nm/RIU with a narrow line width spectral of the plasmon resonances. The figure of merit for this sensor is approximately equal to 14.2 and electrical tuning can be achieved by adjusting the Fermi level in graphene. Therefore, this grating plasmonic structure is highly sensitive and can be used in high resolution biosensing applications.

Surface chemistry and morphology in single particle optical imaging

AbstractBiological nanoparticles such as viruses and exosomes are important biomarkers for a range of medical conditions, from infectious diseases to cancer. Biological sensors that detect whole viruses and exosomes with high specificity, yet without additional labeling, are promising because they reduce the complexity of sample preparation and may improve measurement quality by retaining information about nanoscale physical structure of the bio-nanoparticle (BNP). Towards this end, a variety of BNP biosensor technologies have been developed, several of which are capable of enumerating the precise number of detected viruses or exosomes and analyzing physical properties of each individual particle. Optical imaging techniques are promising candidates among broad range of label-free nanoparticle detectors. These imaging BNP sensors detect the binding of single nanoparticles on a flat surface functionalized with a specific capture molecule or an array of multiplexed capture probes. The functionalization step confers all molecular specificity for the sensor’s target but can introduce an unforeseen problem; a rough and inhomogeneous surface coating can be a source of noise, as these sensors detect small local changes in optical refractive index. In this paper, we review several optical technologies for label-free BNP detectors with a focus on imaging systems. We compare the surface-imaging methods including dark-field, surface plasmon resonance imaging and interference reflectance imaging. We discuss the importance of ensuring consistently uniform and smooth surface coatings of capture molecules for these types of biosensors and finally summarize several methods that have been developed towards addressing this challenge.

Using Transmissive Photonic Band Edge Shift to Detect Explosives: A Study with 2,4,6-Trinitrotoluene (TNT)

Photonic crystals (PhCs) possess outstanding optical properties that can be exploited for chemical sensing. We utilized a three-dimensional close-packed PhC structure made of functionalized silica nanoparticles. They consist of alternating high and low refractive index regions and have optical properties, such as photonic band structures, that are very sensitive to the change of physical structures. This study used 2,4,6-trinitrotoluene (TNT) to illustrate a detection method based on the transmissive photonic band edge shift (TPBES) due to the binding of TNT with amine anchored on particle surfaces to form Meisenheimer (amine-TNT) complexes. PhCs are exceptionally sensitive to a small change in refractive index caused by surface modification. As a result, they are suitable for sensing specific reactions between an amine and TNT. This method achieved a wide detection range of TNT concentrations from 10–12 to 10–4 M. 2,4-Dinitrotoluene (DNT) and toluene were used as a control and blank, respectively. Because of gravitational sedimentation, the TNT-functionalized particles were self-assembled in pure ethanol. They were measured by UV–visible transmission spectroscopy. A three-dimensional model to simulate the detection system was built using the particles’ center-to-center distance (a) and effective dielectric constant (ε) as a function of the TNT concentrations. Two sets of simulations were performed: the first set involved a parametric sweep of the center-to-center distance of TNT-functionalized crystals using ε = 2.015. The second set involved a parametric sweep of the dielectric constant with a = 263.1 nm. These perturbations yield a TPBES response that is in agreement with our experimental results.

1D silicon nitride grating refractive index sensor suitable for integration with CMOS detectors

The transformation of nanophotonic sensors from laboratory-based demonstrations to a portable system to ensure widespread applicability in everyday life requires their integration with detectors for direct electrical read out. As complementary metal oxide semiconductor (CMOS) technology has revolutionized the electronics industry, the integration of nanophotonic structures with CMOS technology will also transform the sensing market. However, nanophotonic sensors have to fulfill certain requirements for their integration with CMOS detectors, such as operation in the visible wavelength range, operation in normal incidence configuration, use of CMOS compatible materials, and capability to give large optical intensity change due to resonance wavelength shift. In this paper, we have designed and developed one-dimensional silicon nitride grating structures that satisfy all these conditions simultaneously. The gratings can achieve 1 and 6 nm linewidths for the transverse-electric (TE) and transverse-magnetic (TM) polarizations, respectively, with 90% resonance depth. The experimental linewidth is 8 nm with 55% resonance depth, which is limited by the detector resolution. The experimental sensitivity of the device is 160 nm/refractive index unit (RIU), which translates to a very high intensity sensitivity of 1700%/RIU, which would enable sensing of very small changes in refractive index when integrated with a detector.